中天山晚奥陶世碰撞造山:来自变质花岗岩地球化学及年代学证据  

Late Ordovician collision and orogen in middle Tianshan: Evidences of geochemical analyses and geochronology on metamorphosed granitoid rocks

作　　者：王行军[1] 王根厚[1] 专少鹏 李广栋[2] 王德强[2] 吴连亨 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]河北省区域地质矿产调查研究所,廊坊065000

出　　处：《岩石学报》2011年第7期2203-2212,共10页Acta Petrologica Sinica

基　　金：地质矿产调查项目(QD200506)资助

摘　　要：中天山包尔图一带发育一套变质变形的花岗岩,属钙碱性系列,其具有较高的Hf和Th含量,而Li、Nb和Ta的含量低;稀土总量中等,具中等铕负异常,稀土配分模式曲线为V型曲线;显示出加里东型I型花岗岩、同碰撞花岗岩的特征。锆石LA-ICP-MSU-Pb测年获得了1207±87Ma、455·6±1·8Ma和433±19Ma3组年龄,其中1207±87Ma代表了碎屑锆石的年龄,说明包尔图一带存在元古宙古老基底;455·6±1·8Ma代表了包尔图岩体的侵位年龄,代表了北天山洋与中天山陆块早古生代一次重要碰撞造山事件;433±19Ma则代表了包尔图岩体侵入岩的后期变质改造年龄,说明早志留世中天山发生过一次变质作用。这次研究的成果对揭示中天山地区的构造演化有着重要的意义。A series of metamorphosed and deformed granitoid rocks occurred in Baoertu area, middle Tianshan of Northwest China. After comprehensive study of petrology, mineralogy and geochemistry, such granitoid rocks are identified as typical calc-alkaline granitoids with following characters： high levels of Hf and Th, lower content of Li , Nb and Ta, the medium REE total, medium negative abnormity of Eu, and V-type REE distribution pattern. All of them indicate that the rocks are Caledon-I type and syn-collision granitoids. Ages of zircon were determined by LA-ICP-MS. Geochronology of U-Pb shows three ages, including 1207±87Ma, 455.6±1.8Ma and 433±19Ma. The first age of 1207±87Ma represents that of clastic zircon, reveals old basement of Proterozoic existed in Baoertu area. The second age of 455.6±1.8Ma indicates Baoertu pluton was intruded in Late Ordovician, which represents an important collision events while northern Tianshan ocean subducted southward beneath the middle Tianshan landmass. In Early Silurian about 433±19Ma, Baoertu pluton was re-built by the metamorphism which indicated a metamorphism had occurred in the area of middle Tianshan, Northwest China. Such results are significant to reveal the tectonic evolution in the area of middle Tianshan, Northwest China.

关 键 词：中天山 碰撞造山 变质花岗岩 地球化学 LA-ICP-MS 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]